The Molecular Biology Core (Core D) consists of two components. 1) The first component (directed by Scott McIvor, Ph.D.) is a proposal to support efforts in retroviral marking of primitive progenitor populations and to use sensitive molecular genetic methods to detect the marked progeny of these progenitors in subsequent hematopoietic cultures, xenotransplants, human autologous and cord blood allogeneic transplants described in projects 1,2,3,4 and 5. The core leader will provide a quality controlled source of retroviral vector for use in transduction experiments and will analyze culture and transplant cell samples to detect presence of the retroviral marker and to identify specific integration events which establish relationships between marked primitive progenitors and their myeloid and lymphoid progeny 2) The second component of Core D (directed by Wesley Miller, M.D) is a proposal to use sensitive molecular genetic methods to assess the presence and extent of contamination with cells containing the BCR/ABL gene rearrangement characteristic of CML in progenitor culture, selected and expanded stem cell inocula and post- transplant patient samples resulting from clinical trials proposed in Project 3 and for CML patients transplanted in project 5. In addition, the two core leaders will combine efforts to detect simultaneously the presence of a retroviral marker and BCR/ABL gene rearrangement in hematopoietic colonies derived from relapsing CML patients following autologous transplantation. These studies will be used to determine the contribution of the selected and expanded primitive progenitor population to recurrence of CML following autologous transplantation. The molecular biology studies described in Core D provide invaluable support to the projects exploring the ontogeny, maintenance and multilineage differentiation of primitive hematopoietic progenitors in vitro and in vivo as well as those exploring the origin of cells responsible for relapse after autologous stem cell transplantation in CML.